US20170260885A1

US20170260885A1 - Camshaft adjuster with a central valve and without a t branch

Info

Publication number: US20170260885A1
Application number: US15/510,533
Authority: US
Inventors: Ali BAYRAKDAR
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2014-09-12
Filing date: 2015-07-08
Publication date: 2017-09-14
Also published as: CN106715843A; DE102014218299A1; WO2016037617A1; DE102014218299B4

Abstract

A hydraulic camshaft adjuster having: a stator with a radially inwardly opening working chamber a rotor arranged radially within the stator, wherein the rotor receives a vane dividing the working chamber into two part chambers, and rotatable relative to the stator about a rotational axis dependent on a hydraulic pressure set in the part chambers . A central valve controls the hydraulic pressure and is configured for selectively connecting individual hydraulic lines which open into the part chambers among one another and/or to a supply line.A check valve device is integrated per part chamber into a first hydraulic line configured in the vane, which check valve device is arranged to act in a permanently closing manner in a first hydraulic flow direction from the central valve into the respective part chamber and can be opened dependent on the hydraulic pressure in a second hydraulic flow direction which is opposed to the first hydraulic flow direction.

Description

The present invention relates to a hydraulic camshaft adjuster of the vane cell type/vane cell design for an internal combustion engine, such as a gasoline engine or diesel engine, of a motor vehicle such as a passenger vehicle, truck, bus, or agricultural utility vehicle, including a stator which is connectable in a rotatably fixed manner to an output shaft of the internal combustion engine and which forms/includes a radially inwardly opening working chamber, a rotor which is situated radially within the stator and connectable to a camshaft of the internal combustion engine, the rotor on the one hand including/accommodating a vane which extends into the working chamber and which divides the working chamber into two subchambers, and on the other hand being rotatable relative to the stator about a rotation axis as a function of a hydraulic pressure that is set in the subchambers, and a central valve which controls the hydraulic pressure and which is designed for selectively connecting individual hydraulic lines, opening into the subchambers, to one another and/or to a supply line.

BACKGROUND

Various camshaft adjusters are already known from the prior art. For example, US 2003/0196625 A1 provides a venting mechanism for devices which vary the camshaft timing. For example, in addition a variable cam timing (VCT) device is provided here, which includes a housing and a rotor that is rotatable relative to this housing. Furthermore, the device also includes a locking element situated essentially in an enclosure in the housing, this locking element closing the housing and the rotor, free from relative rotations and independent of the fluid flow.
In addition, US 2003/0196626 A1 provides a hydraulic lock for a device for changing the camshaft timing. An adjuster includes a housing and once again a rotor that is rotatably situated in the housing. A valve having at least two openings for a fluid flow between a first chamber and a second chamber is designed in such a way that it keeps at least one of the two openings closed. Furthermore, at least one bypass is provided for stopping or decelerating the rotation between the housing and the rotor, thus allowing a closing mechanism to lock the housing and the rotor together, independent of the fluid flow.
DE 11 2011 103 133 T5 provides a camshaft torque-actuated, torsion-assisted adjuster which includes a housing and a rotor that are situated for rotation relative to one another. In addition, the adjuster includes a check valve, and a control valve which includes a spring-loaded control slide that is movable back and forth in the longitudinal direction and that is effectively movable between at least one camshaft torque-actuated (CTA) operating mode, at least one torsion-assisted (TA) operating mode, and at least one zero position, the control slide in various longitudinal positions connecting a first chamber, a second chamber, the check valve, and an actuating fluid supply source to one another.
Furthermore, DE 10 2010 019 530 A1 provides a camshaft adjuster and a U-shaped sealing element for sealing off a radial surface of a vane of the camshaft adjuster.

BACKGROUND

However, the designs known from the prior art are often relatively complex and are usually made up of many individual parts, as the result of which the manufacture of the camshaft adjuster is relatively expensive. In addition, these known designs usually require certain supply pressures for their actuation. In the prior art, either the lines that are present are introduced into the rotor with considerable effort, with a design requiring multiple changes in direction, or the central valve has a relatively complicated design in order to be able to implement the various switching states.
It is an object of the present invention to eliminate these disadvantages from the prior art and provide a camshaft adjuster whose line routing is to be simplified in order to reduce the manufacturing costs, while at the same time retaining a high level of functionality of the camshaft adjuster.
The present invention provides that for each subchamber of the working chamber, a check valve device is integrated into a first hydraulic line that is provided in the vane, the check valve device being situated and configured in such a way that it acts in a continuously blocking manner in a first hydraulic flow direction from the central valve into the particular subchamber, and is openable in a second hydraulic flow direction (from the particular partial working chamber into the central valve) opposite the first hydraulic flow direction, preferably as a function of the hydraulic pressure.
Due to this arrangement of the check valve devices in the vane and their effective direction, the camshaft adjuster has a particularly compact design, and in particular the lines in the rotor are relatively easy to manufacture. The check valve devices typically used for camshaft adjusters are already installed in the vane in a particularly space-saving manner, and the vane, as an individual part, in turn is much more cost-effective to manufacture. In addition, further inlets to and outlets from the central valve are dispensed with, which makes the central valve more cost-effective to manufacture.
Further advantageous specific embodiments are explained in greater detail below.
In addition, it is advantageous when a first check valve device is situated in the first hydraulic line toward one side of a first subchamber of the working chamber. In this regard, it is also advantageous when a second check valve device is situated in the first hydraulic line toward one side of a second subchamber of the working chamber. A particularly space-saving arrangement of the check valve devices is thus facilitated.
If the check valve devices of the subchambers are inserted/integrated/fastened/positioned in/into an inner cavity in the vane, the check valve device may be designed in a particularly cost-effective manner, the check valve device essentially only having to fulfill the function of a check valve. The geometry of the vane and its sealing elements are left unchanged at the outer circumferential side due to the design of the check valve devices. As a result, the particular check valve device as well as the entire camshaft adjuster are manufacturable in a particularly cost-effective manner.
Furthermore, it is also advantageous when each check valve device is designed as a sheet metal part, a sheet metal section of the particular check valve device being elastically bendable in the second hydraulic flow direction. The opening function of the check valve thus has a particularly simple design due to this elastic deformation. In this regard, it is also particularly advantageous when the two check valve devices are part of the same sheet metal part, and are thus designed in the form of sheet metal sections which are an integral part of this one sheet metal part. The camshaft adjuster thus has an even more cost-effective design, and the installation of the check valve devices is even further improved since they are insertable together in the vane.
If the first hydraulic line is connected to the central valve, passing radially inwardly from the vane through the rotor, a particularly direct return of the first hydraulic line to the central valve and a particularly direct control of the camshaft adjuster are provided.
In this regard, it is also advantageous when a second hydraulic line directly connects the first subchamber to the central valve, and/or a third hydraulic line directly connects the second subchamber to the central valve. As a result, additional access lines to the subchambers are provided in order to move the camshaft adjuster into the various positions in a particularly quick and effective manner.
It is also advantageous when the camshaft adjuster (at least in certain operating states/switching states) is designed as a camshaft torque-actuated (CTA) camshaft adjuster, and is thus adjustable as a function of a torque that is applied to the rotor. The camshaft adjuster is thus designable/designed without an additional tank connection, thus further simplifying the manufacture of the camshaft adjuster.
It is also advantageous when the supply line is connectable to a pump that conveys a hydraulic medium in the direction of the central valve, a third check valve device being integrated into the supply line between the pump and the central valve. The supply line and the pump may thus likewise be connected to the central valve, depending on the position of the check valve, and in certain switching states the central valve may thus be directly supplied with the control pressure of the pump. A camshaft adjuster is thus provided which operates particularly efficiently in certain switching states as a CTA camshaft adjuster, and in other switching states as an oil pressure-activated (OPA) camshaft adjuster. A particularly efficient camshaft adjuster is provided in this way.
In other words, a camshaft adjuster in the form of a variable cam timing (VCT) system is thus implemented, the central valve including no T port/T branch. Oil/hydraulic medium is diverted between the two chambers (subchambers) by passing through a check valve (check valve devices) situated in the vane between these two chambers. The extending chamber is connected to the P port (of the supply line), and the oil/hydraulic medium of the chamber, which is decreasing in size, is connected to the oppositely situated chamber. Pressure differences upstream and downstream from the check valve control the flow of the oil/hydraulic medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail below with reference to the figures, in conjunction with which various specific embodiments are also explained.

FIG. 1 shows a cross-sectional illustration of a camshaft adjuster according to the present invention according to a first specific embodiment, in particular the configuration and the design of the first hydraulic line in the vane and in the rotor being apparent, and the pressure fluid flowing in a second hydraulic flow direction being denoted by an arrow;

FIG. 2 shows the same cross-sectional illustration of the camshaft adjuster illustrated in FIG. 1, but with the hydraulic medium now being depicted as flowing or pushing in the first hydraulic flow direction;

FIG. 3 shows a longitudinal section illustration of the camshaft adjuster according to the present invention according to FIG. 1, in which the arrangement of the camshaft adjuster at one end of a camshaft is particularly clearly apparent, and an adjustment actuator that acts on the central valve is apparent, the section plane extending along the rotation axis of the camshaft adjuster;

FIG. 4 shows a longitudinal section illustration of the camshaft adjuster according to the first specific embodiment, the illustration being similar to FIG. 3, except that the camshaft adjuster together with the camshaft are now sectioned in a plane that is rotated with respect to the section plane in FIG. 3;

FIG. 5 shows a detailed view of the camshaft adjuster according to the present invention in the section according to FIG. 3, the various flow directions that are settable by the central valve inside the camshaft adjuster being denoted by arrows for better clarity;

FIG. 6 shows a detailed view of the camshaft adjuster according to the present invention in the section according to FIG. 4, in this case the rotor being sectioned in an angular range in which the first hydraulic line is situated, and once again a flow arrow being illustrated which depicts a push of hydraulic medium from the supply line, via the central valve, toward the check valve;

FIG. 7 shows a detailed view of the central valve in a section area as illustrated in FIG. 6, the various flow directions and flow conditions within the central valve being particularly clearly apparent, and the supply line on the side of the pump being connected to the interior of the central valve; and

FIG. 8 shows a detailed view of the central valve in a section area as illustrated in FIG. 5, the central valve being in that position in which the first subchamber is connected to the central valve, but the second subchamber is blocked with respect to the first subchamber, so that the two subchambers are also decoupled from one another.

DETAILED DESCRIPTION

The figures are merely schematic, and are used only for an understanding of the present invention. Identical elements are provided with the same reference numerals.
The basic design of hydraulic camshaft adjuster 1 according to the present invention is particularly clearly apparent in conjunction with FIGS. 1 through 4. Hydraulic camshaft adjuster 1 has a design of the vane cell construction/vane cell type. Camshaft adjuster 1 according to the present invention has essentially the same design and function as the camshaft adjuster in DE 10 2010 019 530 A1 so that this publication is considered to be incorporated by reference herein.
As is customary, hydraulic camshaft adjuster 1 includes a stator 2 with means, namely, external teeth, which are designed for connection to a traction mechanism drive in a rotatably fixed manner. In the operating state of an internal combustion engine, this stator 2 is thus connected to an output shaft of the internal combustion engine in a rotatably fixed manner. Stator 2 has a radially inwardly opening working chamber 3. Upon further inspection, it is apparent that stator 2 has not just one working chamber 3, but, rather, has four working chambers 3, which are spaced apart from one another along the circumference (of stator 2). A vane 7 connected to a rotor 6 is accommodated within each of these geometrically separated working chambers 3. Rotor 6 is in turn radially supported so that it is rotatable within stator 2. Vane 7, which is situated on an outer side/outer circumferential side of rotor 6 in a rotatably fixed manner, in turn extends into working chamber 3 in the radial direction. Vane 7 protrudes into working chamber 3 associated with it in such a way that vane 7 divides working chamber 3 into two partial working chambers/ subchambers 4 and 5 that are independently hydraulically controllable.
In the operating state of the internal combustion engine/camshaft adjuster 1, rotor 6 is in turn connected to a camshaft 23 of the internal combustion engine in a rotatably fixed manner, as is customary. Upon further inspection, it is apparent that rotor 6 has one vane 7 for each working chamber 3 of stator 2, with only one vane 7 being inserted/protruding into each working chamber 3. Vane 7 is in sealing contact with stator 2, so that in the operating state, the two partial working chambers 4 and 5 of a working chamber 3 are sealed and fillable with hydraulic medium independently of one another. Camshaft adjuster 1 is thus adjusted/set as a function of the set hydraulic pressure in subchambers 4 and 5. Rotor 6 is set in the desired rotary position relative to stator 2 about a rotation axis 8 (FIG. 3) as a function of the hydraulic pressure.
In addition, camshaft adjuster 1 includes a central valve 9 which is designed for selectively connecting the individual hydraulic lines 10, 11, 12, opening into subchambers 4 and 5, to one another or to a supply line 13. Central valve 9 controls the relative rotary position that is to be achieved between rotor 6 and stator 2, as a function of the position of the central valve/the position of its piston 16 which is displaceable in the axial direction, and allows the desired hydraulic pressure to be set in the particular subchamber 4 or 5.
A first hydraulic line 10 is introduced into each vane 7; in the discussion below, only one vane 7, one working chamber 3 associated with this vane 7, and the two subchambers 4 and 5 associated with this working chamber 3 are described by way of example. First hydraulic line 10 extends within vane 7 essentially in a straight line in the radial direction. First hydraulic line 10 merges into rotor 6 at a radial inner side of vane 7 in the area where vane 7 is connected to rotor 6. First hydraulic line 10 is therefore introduced with a first (radially outer) section into vane 7, and is introduced with a second (radially inner) section into rotor 6. First hydraulic line 10 extends through rotor 6 in the radial direction, and is open at an inner side of rotor 6 facing central valve 9. When central valve 9 is installed, it is therefore connected to this first hydraulic line 10.
First hydraulic line 10 is divided into two line portions 18 and 19 in vane 7. A line portion 18 or 19 opens into a subchamber 4 or 5, respectively. In FIG. 1, first hydraulic line 10 opens into first subchamber 4 with a first line portion 18 extending along the circumference in the counterclockwise direction, and opens into second subchamber 5 with a second line portion 19 extending along the circumference in the clockwise direction.
In the transition area between first hydraulic line 10 and first subchamber 4, i.e., in first line portion 18, a first check valve device 14 is situated/installed/inserted in vane 7, and in the transition area between first hydraulic line 10 and second subchamber 5, i.e., in second line portion 19, a second check valve device 15 is situated/installed/inserted in vane 7.
Each check valve device 14 and 15 acts as a check valve. Each check valve device 14 and 15 is formed by a sheet metal section 20 or 21. Both sheet metal sections 20 and 21 are an integral part of a sheet metal part which essentially has a bracket/pear/Ω shape. Each of sheet metal sections 20 and 21 is designed as a strip-shaped sheet metal section 20 or 21 that is elastically deformable/bendable. Sheet metal sections 20 and 21 are situated and configured in such a way that they open only beginning at a certain pressure difference between first hydraulic line 10 and the particular subchamber 4 and 5, when a hydraulic fluid is pushed from the particular subchamber 4 and 5 into first hydraulic line 10. This direction is referred to as the second hydraulic flow direction. In turn, during operation of camshaft adjuster 1, sheet metal sections 20 and 21 have a continuously blocking action in a first hydraulic flow direction that is opposite this second hydraulic flow direction. In other words, check valve devices 14 and 15 are designed in the form of a sheet metal part that is configured essentially as a sheet metal bracket. This sheet metal part is inserted into a cavity 22 inside vane 7, namely, snapped in place/locked in place, for example, and is therefore held in a form-fit and/or force-fit manner.
First sheet metal section 20 is thus designed as first check valve device 14, and is situated in such a way that it elastically deforms and allows a hydraulic medium flow from first subchamber 4 into first hydraulic line 10 when the pressure within first subchamber 4 is greater than in first hydraulic line 10. The hydraulic medium then flows from first subchamber 4, via first sheet metal strip 20 which is then deformed, into first hydraulic line 10 and thus to central valve 9. If the hydraulic pressure within second subchamber 5 is higher than in first hydraulic line 10 in another position of camshaft adjuster 1, as illustrated in FIG. 1, second sheet metal section 21 is elastically deformed in such a way that it allows a hydraulic medium flow from second subchamber 5 into first hydraulic line 10 and thus toward central valve 9. In this additional position, hydraulic medium may thus flow from second subchamber 5 into central valve 9, from where it is then fed into first subchamber 4. The two sheet metal sections 20 and 21 thus directly take on the function of the check valve.
In the first hydraulic flow direction, as is clearly apparent in FIG. 2, these two sheet metal sections 20 and 21 then act once again in such a way that they are positioned so that they close/seal off the particular line portions 18 and 19 and prevent/block flow of a hydraulic medium from first hydraulic line 10 into the particular subchamber 4 or 5.
As is also particularly clearly apparent in FIG. 4, first hydraulic line 10 extends essentially centrally, i.e., centrally in the axial direction of the rotor. First hydraulic line 10 is designed as a linear borehole that extends from vane 7 toward central valve 9. For each subchamber 4 and 5, an additional hydraulic line 11 or 12 extends from central valve 9 into subchamber 4 or 5, respectively, next to first hydraulic line 10. First subchamber 4 is connected directly to central valve 9 with the aid of a second hydraulic line 11 that extends inwardly in the radial direction, and second subchamber 5 is connected directly to central valve 9 with the aid of a further, third hydraulic line 12 that extends inwardly in the radial direction. The various hydraulic lines 10, 11, and 12 are particularly clearly apparent in FIG. 5; their directions of extension are provided with the associated reference arrows. A first reference arrow denoted by reference numeral 24 depicts the direction of extension of first hydraulic line 10. A second reference arrow denoted by reference numeral 25 depicts the direction of extension of second hydraulic line 11. A third reference arrow denoted by reference numeral 26 depicts the direction of extension of third hydraulic line 12.
Supply line 13 adjoining central valve 9 extends further to a pump, not illustrated here for the sake of clarity, and into the interior of central valve 9. With the aid of a third check valve device 17 which likewise is designed as a check valve, the first section of supply line 13, which extends outside of central valve 9, may be blocked with respect to a second section of supply line 13 that extends within central valve 9. Supply line 13 thus connects the pump/supply pump directly to the interior of central valve 9 as a function of the position of third check valve device 17. Third check valve device 17 acts in such a way that from the pump, it opens in a first flow direction of hydraulic medium (denoted by fourth reference arrow 27) into central valve 9 and into the particular hydraulic lines 10, 11, 12, beginning at a certain, higher hydraulic pressure in the first section with respect to the interior of central valve 9/the second section (FIGS. 6 and 7). Third check valve device 17 permanently blocks in a second flow direction opposite this first flow direction, i.e., out of the central valve and toward the pump (FIGS. 5 and 8). As illustrated in FIG. 7, in a first operating position/a first operating state it is thus possible to always supply the interior of central valve 9 with the desired operating pressure, and to use camshaft adjuster 1 as an OPA camshaft adjuster. On the other hand, as is particularly clearly apparent in FIG. 8, in a second operating position/a second operating state it is possible to decouple the interior of central valve 9 from the pump, and via second and third hydraulic lines 11 and 12 to control subchambers 4 and 5 independently of the operating pressure specified by the pump, in which case camshaft adjuster 1 is then used as a CTA camshaft adjuster.
In other words, unlike the case for the adjusters known thus far, at least one rotor vane (vane 7) is provided with a check valve 14, 15 in the interior of camshaft adjuster 1 of the type according to the present invention. Two check valves 14, 15 are integrated into each vane 7. Check valve 14, 15 is situated in vane 7, and may open and close in both directions (from first subchamber 4 into first hydraulic line 10 and from second subchamber 5 into first hydraulic line 10), depending on the pressure difference. Check valve 14, 15 radially conducts the transmitted oil/hydraulic medium from chamber A (first subchamber 4) or chamber B (second subchamber 5) into central valve 9, and is thus connected to oil channel P (supply channel/pressure channel/supply line 13). Rotor 6 includes a third oil channel (first hydraulic line 10, a so-called R channel). The third oil channel is situated in the axial center, but may also be situated outside, i.e., not in the axial center. Adjuster 1 does not include a T branch (tank outlet). The mode of operation may be explained as follows: Adjuster 1 and central valve 9 are initially filled at a fairly low oil pressure, so that no air is in the system. No T branch is present in the system; i.e., for the oil filling it is sufficient when the oil expels the air that is present, via leakage. If an excess pressure, which arises due to alternating torques, occurs in chamber A or B, check valves 14, 15 become active and allow excess pressure to escape through central valve 9 to the P channel (supply line 13) in central valve 9. Since the pressure is not able to flow back out of central valve 9, namely, toward the pump, on account of the central valve check valve (third check valve device 17), excess pressure is introduced into chamber A or B (subchamber 14 and 15). If an excess pressure should arise in chambers A (14) or B (15) due to an alternating torque, and which is not intended to be adjusted, the excess pressure may be introduced via oil channel A (11) or oil channel B (12) back into central valve 9, and there may be introduced into P chamber (13) or R chamber (10). This results in equal pressures everywhere, and check valve 14, 15 is no longer able to open, also due to the elastic pretension. Hydraulic support is thus provided, and adjuster 1 is no longer able to move in an unintended direction. Central valve 9 is provided with additional channel R (first hydraulic line 10), which is connected directly to P channel (supply line 13/first section of supply line 13). Since oil migration between the A chamber and B chamber develops and no oil exits the tank, adjuster system 1 requires no additional supply pressures. This is necessary only for the supply pressure that has been lost to the outside due to leakage. There would be no oil loss if an even more leak-proof adjuster system were implemented. In turn, this saves additional effort for the engine design. The T branch is not necessary in the design of central valve 9. This dispenses with, for example, a large number of boreholes on the piston head (valve slide). It is sufficient to provide a fairly small opening/borehole in order to vent the clearance space behind the piston. At the same time, the third and fourth control windows are dispensed with. Two control edges on the piston and two control edges on the housing are no longer required. This in turn saves on costs in manufacturing the individual parts.

LIST OF REFERENCE NUMERALS

1 camshaft adjuster
2 stator
3 working chamber
4 first subchamber
5 second subchamber
6 rotor
7 vane
8 rotation axis
9 central valve
10 first hydraulic line
11 second hydraulic line
12 third hydraulic line
13 supply line
14 first check valve device
15 second check valve device
16 piston
17 third check valve device
18 first line portion
19 second line portion
20 first sheet metal section
21 second sheet metal section
22 cavity
23 camshaft
24 first reference arrow
25 second reference arrow
26 third reference arrow
27 fourth reference arrow

Claims

1-10. (canceled)

11. A vane cell hydraulic camshaft adjuster comprising:

a stator with a radially inwardly opening working chamber;

a rotor situated radially within the stator, the rotor accommodating a vane extending into the working chamber dividing the working chamber into first and second subchambers, the rotor being rotatable relative to the stator about a rotation axis as a function of a hydraulic pressure set in the first and second subchambers, and a central valve controlling the hydraulic pressure and designed for selectively connecting individual hydraulic lines, opening into the first and second subchambers to one another or to a supply line;

for each of the first and second subchambers, a respective check valve device being integrated into a first hydraulic line provided in the vane so as to define first and second check valve devices, the first and second check valve devices being situated to act in a permanently blocking manner in a first hydraulic flow direction from the central valve into the respective first or second subchamber, and openable in a second hydraulic flow direction opposite the first hydraulic flow direction.

12. The camshaft adjuster as recited in claim 11 wherein first check valve device is situated in the first hydraulic line toward one side of the first subchamber.

13. The camshaft adjuster as recited in claim 11 wherein the second check valve device is situated in the first hydraulic line toward one side of the second subchamber.

14. The camshaft adjuster as recited in claim 11 wherein the first and second check valve devices are inserted into an inner cavity of the vane.

15. The camshaft adjuster as recited in claim 11 wherein each of the first and second check valve devices is designed as a sheet metal part, a sheet metal section of the particular first or second check valve device being elastically bendable in the second hydraulic flow direction.

16. The camshaft adjuster as recited in claim 11 wherein the first hydraulic line is connected to the central valve, passing radially inwardly from the vane through the rotor.

17. The camshaft adjuster as recited in claim 11 wherein a second hydraulic line directly connects the first subchamber to the central valve.

18. The camshaft adjuster as recited in claim 11 wherein a third hydraulic line directly connects the second subchamber to the central valve.

19. The camshaft adjuster as recited in claim 11 wherein the supply line is connectable to a pump conveying a hydraulic medium in the direction of the central valve, a third check valve device being integrated into the supply line.

20. The camshaft adjuster as recited in claim 11 wherein the camshaft adjuster is adjustable as a function of a torque applied to the rotor.